¹Department of Biotechnology and Molecular Medicine, AI Virtanen Institute for Molecular Sciences, University of Kuopio, Kuopio, Finland

Correspondence: Dr O Rautsi, Department of Biotechnology and Molecular Medicine, AI Virtanen Institute for Molecular Sciences, University of Kuopio, PO Box 1627, Kuopio FI-70211, Finland. E-mail: outi.rautsi@uku.fi

²Present address: Institute of Medical Technology, University of Tampere, FI-33014 Tampere, Finland

³Present address: Academic Development Unit, University of Tampere, FI-33014 Tampere, Finland

Received 8 June 2007; Revised 16 December 2007; Accepted 18 January 2008; Published online 29 February 2008.

Abstract

Cancer suicide gene therapy based on herpes simplex virus type I thymidine kinase (HSV-TK) and ganciclovir (GCV) suffers from the lack of efficacy in clinical use, which is mostly due to low gene-transfer efficiency and absence of bystander effect in tumors. We have previously demonstrated the enhancement of GCV cytotoxicity by fusing the HSV-TK with the cell penetrating peptide from HIV-1 transactivator protein transduction domain (TAT PTD). Despite the earlier promising results, we found that the triple fusion protein HIV-1 transactivator protein transduction domain–thymidine kinase suicide gene–green fluorescent protein marker gene (TAT-TK-GFP) increased GCV cytotoxicity only in 3/12 of different human tumor cell lines. Extended GCV exposure enhanced the cytotoxic effect of HSV-TK/GCV gene therapy, but the difference between TK-GFP and TAT-TK-GFP was not statistically significant. The modest improvement on cell killing mediated by TAT PTD in Chinese hamster ovary cells appeared to be associated with cell-surface heparan sulfate proteoglycan (HSPG) composition. However, TAT-mediated increased cell death did not correlate with the density of cell-surface HSPG expression in different tumor cell lines. In conclusion, although some degree of enhancement by TAT was shown in certain tumor cells in vitro, it is unlikely that TAT peptide linked to a suicide protein could be a useful booster of in vivo gene therapy trials.